In Wright Patterson base commander General Curtis Lemay's autobiography, he admitted, that some cases in Bluebook were unidentified & anomalous. That was in 1965 prior to Bluebook ending in 1969. New Govt documents from CIA, Navy, NASA & others are exposing the internal Govt struggle with what was coined, "The UFO Problem." Yet there are cracks all throughout history in various documents & autobiographies.

"The bulk of them could be run down. Some natural phenomenon might usually account for those sightings which had been seen and reported, and thus explain them. However, we had a number of reports from reputable individuals (well-educated, serious-minded folks—scientists and fliers) who surely saw something.
There is no question about it: these were things which we could not tie in with any natural phenomena known to our investigators."
~General Curtis "Rand Corp" Lemay.